1. Field of the Invention
This invention relates to an optical disc as represented by compact discs (CD), laser video discs (LVD), particularly to an optical disc by the Photo-Polymer method (2P method), a process for producing the same and a reading method.
2. Description of the prior art
As a representative method for preparation of an optical disc, there has been known the Photo-Polymer method which duplicates a disc by use of a polymer which is cured by UV-ray irradiation (UV-ray curable resin).
More specifically, this method comprises filling or coating a UV-ray curable resin between a stamper (mold) having uneven pits with a predetermined memorized information and a transparent substrate which becomes the disc base, curing said resin by irradiation with a UV-ray, then peeling off the stamper to form a recording layer having uneven pits on the transparent substrate, forming a metallic reflective film on the uneven pit surface by such means as vapor deposition or sputtering of a metal, and further forming a protective film, thereby forming an optical disc.
The optical disc is adapted to reproduce the information memorized by permitting an optical signal such as laser beam, etc. to enter from the transparent substrate side and reading the reflected light signal from the metallic reflective film.
The optical disc prepared as described above permits a light such as a laser beam, etc. to enter from the transparent substrate side, pass through the recording layer and reach the reflective film. In this case, however, the reflectance of the laser beam is not sufficiently high, and moreover, there is a problem that the surface reflectance at the concavity in the uneven pits formed by the metallic reflective film is considerably different from that at the convexity.
Thus, since in an optical disc, lightness and darkness due to phase difference between the reflected lights from the above-mentioned concavity and convexity is grasped as the signal to perform reproduction of the memorized information, such remarkable difference in reflectance between the concavity and the convexity will lead to many bit errors so as to bring about a very undesirable deterioration in quality of the information reproduced (e.g., sound or image).